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            <ol class="post-toc"><li class="post-toc-item post-toc-level-3"><a class="post-toc-link" href="#今天刷C语言程序题时遇到很多关于static关键字的题目-为区分Java中的static继而回到寝室写一篇关于Java中static关键字的使用详解"><span class="post-toc-number">1.</span> <span class="post-toc-text">今天刷C语言程序题时遇到很多关于static关键字的题目,为区分Java中的static继而回到寝室写一篇关于Java中static关键字的使用详解.</span></a></li><li class="post-toc-item post-toc-level-3"><a class="post-toc-link" href="#先来谈谈Java中的static"><span class="post-toc-number">2.</span> <span class="post-toc-text">先来谈谈Java中的static</span></a><ol class="post-toc-child"><li class="post-toc-item post-toc-level-4"><a class="post-toc-link" href="#static-变量"><span class="post-toc-number">2.1.</span> <span class="post-toc-text">static 变量</span></a></li><li class="post-toc-item post-toc-level-4"><a class="post-toc-link" href="#static-方法"><span class="post-toc-number">2.2.</span> <span class="post-toc-text">static 方法</span></a></li><li class="post-toc-item post-toc-level-4"><a class="post-toc-link" href="#static-代码块"><span class="post-toc-number">2.3.</span> <span class="post-toc-text">static 代码块</span></a></li><li class="post-toc-item post-toc-level-4"><a class="post-toc-link" href="#使用JDBC中简单的Data-access-obejct实例来讲解如何利用static关键字优化程序性能-っ•̀ω•́-っ✎⁾⁾"><span class="post-toc-number">2.4.</span> <span class="post-toc-text">使用JDBC中简单的Data access obejct实例来讲解如何利用static关键字优化程序性能 ! (っ•̀ω•́)っ✎⁾⁾</span></a></li></ol></li></ol>
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            <h3 id="今天刷C语言程序题时遇到很多关于static关键字的题目-为区分Java中的static继而回到寝室写一篇关于Java中static关键字的使用详解"><a href="#今天刷C语言程序题时遇到很多关于static关键字的题目-为区分Java中的static继而回到寝室写一篇关于Java中static关键字的使用详解" class="headerlink" title="今天刷C语言程序题时遇到很多关于static关键字的题目,为区分Java中的static继而回到寝室写一篇关于Java中static关键字的使用详解."></a>今天刷C语言程序题时遇到很多关于<code>static</code>关键字的题目,为区分Java中的<code>static</code>继而回到寝室写一篇关于Java中<code>static</code>关键字的使用详解.</h3><h3 id="先来谈谈Java中的static"><a href="#先来谈谈Java中的static" class="headerlink" title="先来谈谈Java中的static"></a>先来谈谈Java中的<code>static</code></h3><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="string">"static方法就是没有this的方法.在static方法内部不能调用非静态方法,反过来是可以的.而且可以在没有创建任何对象的前提下,仅仅通过类本身来调用static方法.这实际上正是static方法的主要用途.   ———— 《 Java编程思想 》"</span></span><br><span class="line"></span><br><span class="line">总结为一句话：方便在没有创建对象的情况下来进行调用(方法/变量).</span><br></pre></td></tr></table></figure>
<ul>
<li><h4 id="static-变量"><a href="#static-变量" class="headerlink" title="static 变量"></a><code>static</code> 变量</h4><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">static</span> 变量也称作静态变量.</span><br><span class="line">静态变量:   静态变量被所有的对象所共享,在内存中只有一个副本.它当且仅当在类初次加载时会被初始化.</span><br><span class="line">非静态变量: 是对象所拥有的,在创建对象的时候被初始化.存在多个副本,各个对象拥有的副本互不影响.</span><br></pre></td></tr></table></figure>
</li>
<li><h4 id="static-方法"><a href="#static-方法" class="headerlink" title="static 方法"></a><code>static</code> 方法</h4><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">使用 <span class="keyword">static</span> 修饰的方法一般称作静态方法.由于静态方法不依赖于任何对象就可以进行访问,因此对于静态方法来内说是无法使用 <span class="keyword">this</span> 关键字的,</span><br><span class="line">因为它不依附于任何对象,既然都没有对象,就谈不上 <span class="keyword">this</span> 了 ! 继而由于这个特性,在静态方法中不能访问类的非静态成员变量和非静态成员方法,</span><br><span class="line">因为非静态成员方法/变量都是必须依赖具体的`对象`才能够被调用.</span><br></pre></td></tr></table></figure>
</li>
<li><h4 id="static-代码块"><a href="#static-代码块" class="headerlink" title="static 代码块"></a><code>static</code> 代码块</h4><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">静态代码块以优化程序性能.<span class="keyword">static</span> 块可以置于类中的任何地方,类中可以有多个<span class="keyword">static</span>块.</span><br><span class="line">在类初次被加载的时候,会按照 <span class="keyword">static</span> 代码块的顺序逐个执行,并且只会执行一次.</span><br></pre></td></tr></table></figure>
</li>
</ul>
<h4 id="使用JDBC中简单的Data-access-obejct实例来讲解如何利用static关键字优化程序性能-っ•̀ω•́-っ✎⁾⁾"><a href="#使用JDBC中简单的Data-access-obejct实例来讲解如何利用static关键字优化程序性能-っ•̀ω•́-っ✎⁾⁾" class="headerlink" title="使用JDBC中简单的Data access obejct实例来讲解如何利用static关键字优化程序性能 ! (っ•̀ω•́)っ✎⁾⁾"></a>使用JDBC中简单的<code>Data access obejct</code>实例来讲解如何利用<code>static</code>关键字优化程序性能 ! (っ•̀ω•́)っ✎⁾⁾</h4><ol>
<li><p>首先创建一个连接数据库的工具类,使用<code>static 代码块</code>解决重复加载驱动问题,提高性能.</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: JDBCUtil</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: Connect to the database.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: Huang Yuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: Mar 13, 2019 3:19:41 PM</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">JDBCUtil</span> </span>&#123;</span><br><span class="line">	</span><br><span class="line">	<span class="function"><span class="keyword">private</span> <span class="title">JDBCUtil</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		<span class="comment">// TODO Auto-generated constructor stub</span></span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="comment">// initialize the driver of database.</span></span><br><span class="line">	<span class="keyword">static</span> &#123;</span><br><span class="line">		<span class="keyword">try</span> &#123;</span><br><span class="line">			Class.forName(<span class="string">"com.mysql.cj.jdbc.Driver"</span>);</span><br><span class="line">		&#125; <span class="keyword">catch</span> (ClassNotFoundException e) &#123;</span><br><span class="line"></span><br><span class="line">			e.printStackTrace();</span><br><span class="line">		&#125;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">	<span class="comment">// Return a database connection object.</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> Connection <span class="title">getConnection</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		Connection connection = <span class="keyword">null</span>;</span><br><span class="line">		<span class="keyword">try</span> &#123;</span><br><span class="line">			connection = DriverManager.getConnection(<span class="string">"jdbc:mysql://localhost/databaseName?"</span></span><br><span class="line">					+ <span class="string">"useSSL=false&amp;serverTimezone=UTC&amp;allowPublicKeyRetrieval=true"</span>, <span class="string">"username"</span>, <span class="string">"password"</span>);</span><br><span class="line">		&#125; <span class="keyword">catch</span> (SQLException e) &#123;</span><br><span class="line">			e.printStackTrace();</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">return</span> connection;</span><br><span class="line">	&#125;</span><br><span class="line">	</span><br><span class="line">	<span class="comment">// release the resource of connecting.</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">freeResource</span><span class="params">(Connection connection,PreparedStatement preparedStatement,ResultSet resultSet)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">if</span>(connection!=<span class="keyword">null</span>) &#123;</span><br><span class="line">			<span class="keyword">try</span> &#123;</span><br><span class="line">				connection.close();</span><br><span class="line">			&#125; <span class="keyword">catch</span> (SQLException e) &#123;</span><br><span class="line">				</span><br><span class="line">				e.printStackTrace();</span><br><span class="line">			&#125;</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">if</span>(preparedStatement!=<span class="keyword">null</span>) &#123;</span><br><span class="line">			<span class="keyword">try</span> &#123;</span><br><span class="line">				preparedStatement.close();</span><br><span class="line">			&#125; <span class="keyword">catch</span> (SQLException e) &#123;</span><br><span class="line">	</span><br><span class="line">				e.printStackTrace();</span><br><span class="line">			&#125;</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">if</span>(resultSet!=<span class="keyword">null</span>) &#123;</span><br><span class="line">			<span class="keyword">try</span> &#123;</span><br><span class="line">				resultSet.close();</span><br><span class="line">			&#125; <span class="keyword">catch</span> (SQLException e) &#123;</span><br><span class="line">				</span><br><span class="line">				e.printStackTrace();</span><br><span class="line">			&#125;</span><br><span class="line">		&#125;</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p>利用<code>static</code>修饰单独抽取出来的<code>Connection</code>对象使其成为静态变量.继而使得整个<code>DAO</code>可以共享此对象.</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: basicConnection</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: Share this object of Connection.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: Huang Yuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: Mar 13, 2019 3:15:43 PM</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">basicConnection</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	<span class="keyword">public</span> <span class="keyword">static</span> Connection connection = JDBCUtil.getConnection();</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p>小哥就简写一下<code>DAO</code>层类,便于举例: 增加数据表信息的类 + 删除数据表信息的类 + ······</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: basicConnectionTest</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: Insert the specified data into the database.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: Huang Yuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: Mar 16, 2019 10:40:11 PM</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">InsertTest</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	Connection connection = basicConnection.connection;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Test</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">insertInfoTest</span><span class="params">()</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">		System.out.println(<span class="string">"insertInfoTest : "</span> + connection);</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: DeleteTest</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: Delete the specified data from the database.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: Huang Yuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: Mar 16, 2019 11:05:44 PM</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">DeleteTest</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	Connection connection2 = basicConnection.connection;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Test</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">deleteInfoTest</span><span class="params">()</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">		System.out.println(<span class="string">"deleteInfoTest : "</span> + connection2);</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<ol start="4">
<li><p>利用<code>JUnit</code>测试套件测试<code>Data acess object</code>中所有的测试类.</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: AllTest</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: Test all class.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: Huang Yuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: Mar 16, 2019 11:04:58 PM</span></span><br><span class="line"><span class="comment"> * </span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="meta">@RunWith</span>(Suite<span class="class">.<span class="keyword">class</span>)</span></span><br><span class="line"><span class="class">@<span class="title">SuiteClasses</span>(</span>&#123; InsertTest<span class="class">.<span class="keyword">class</span>, <span class="title">DeleteTest</span>.<span class="title">class</span> &#125;)</span></span><br><span class="line"><span class="class"><span class="title">public</span> <span class="title">class</span> <span class="title">AllTest</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p>输出结果如下所示.由于<code>Connection</code>对象被抽取且被<code>static</code>修饰为了静态对象.继而在整个<code>DAO</code>中可以共享这个<code>连接数据库的对象</code>.而不必每一个类中都实例化一次<code>连接数据库的对象(Connection)</code>继而提升程序的性能（づ￣3￣）づ╭❤～</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">insertInfoTest : com.mysql.cj.jdbc.ConnectionImpl@<span class="number">158</span>a8276</span><br><span class="line">deleteInfoTest : com.mysql.cj.jdbc.ConnectionImpl@<span class="number">158</span>a8276</span><br></pre></td></tr></table></figure>
</li>
</ol>
<ul>
<li><em>哎哟,不知觉又半夜啦! 晚安,好梦. remember love yourself deeply.</em></li>
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